Numerous surface-active agents are already known. They are used in many branches of industry for wetting solid surfaces with aqueous solutions or for dispersing liquids and/or solids in water. Thus, ethylene oxide/propylene oxide-based polyether diols synthesized from discrete polypropylene oxide and polyethylene oxide blocks are used in this field. Although products such as these are used for numerous applications, they can only be used to a limited extent at most in emulsion polymerization. In the field of emulsion polymerization there is an ongoing search for new surface-active agents which have favorable properties for the preparation of the emulsion; for the emulsion polymerization process; and especially with respect to the properties of the polymer latex formed by the polymerization process. In general, those skilled in this art are unable to use the chemical structure of a surface-active agent to predict its properties as a polymerization emulsifier. In industrial terms, particularly valuable emulsifiers are those which, through emulsion polymerization, make it possible to obtain finely divided, coagulate-free foam-poor latices which can be dried to form substantially water-resistant polymer films or compositions.